$\dfrac{3}{2} - \dfrac{7}{10} = {?}$
$ = {\dfrac{3 \times 5}{2 \times 5}} - {\dfrac{7 \times 1}{10 \times 1}} $ $ = {\dfrac{15}{10}} - {\dfrac{7}{10}} $ $ = \dfrac{{15} - {7}}{10} $ $ = \dfrac{8}{10}$